ABSTRACT
We have studied the effect of doping of both magnetic (Co) and nonmagnetic (Mg) ions at the Cu site on phase transition in polycrystalline α-Cu2V2O7through structural, magnetic, and electrical measurements. X-ray diffraction reveals that Mg doping triggers an onset ofα- toß-phase structural transition in Cu2-xMgxV2O7above a critical Mg concentrationxc= 0.15, and both the phases coexist up tox= 0.25. Cu2V2O7possesses a non-centrosymmetric crystal structure and antiferromagnetic ordering along with a non-collinear spin structure in theαphase, originated from the microscopic Dzyaloshinskii-Moriya interaction between the neighboring Cu spins. Accordingly, a weak ferromagnetic (FM) behavior has been observed up tox= 0.25. However, beyond this concentration, Cu2-xMgxV2O7exhibits complex magnetic properties. A clear dielectric anomaly is observed in α-Cu2-xMgxV2O7around the magnetic transition temperature, which loses its prominence with the increase in Mg doping. The analysis of experimental data shows that the magnetoelectric coupling is nonlinear, which is in agreement with the Landau theory of continuous phase transitions. Co doping, on the other hand, initiates a sharpαtoßphase transition around the same critical concentrationxc= 0.15 in Cu2-xCoxV2O7but the FM behavior is very weak and can be detected only up tox= 0.10. We have drawn the magnetic phase diagram which indicates that the rate of suppression in transition temperature is the same for both types of doping, magnetic (Co) and nonmagnetic (Zn/Mg).
ABSTRACT
Highly packed LN-type ZnSnO3 NW arrays are grown on ZnO:Al/Si substrates using a hybrid pulsed laser deposition and solvothermal process. Unique "welding" mechanism structurally joins adjacent ZnSnO3 NWs to form a nearly impervious 20 µm thick nanostructured film that shows high P r of 30 µC/cm(2) at a low E c of 25 kV/cm for the first time.
ABSTRACT
Highly textured cobalt ferrite (CFO) thin films were grown on Si (100) substrates using oblique-angle pulsed laser deposition (α-PLD). X-ray diffraction and in-depth strain analysis showed that the obliquely deposited CFO films had both enhanced orientation in the (111) crystal direction as well as tunable compressive strains as a function of the film thicknesses, in contrast to the almost strain-free polycrystalline CFO films grown using normal-incidence PLD under the same conditions. Using in situ optical plume diagnostics the growth parameters in the α-PLD process were optimized to achieve smoother film surfaces with roughness values as low as 1-2 nm as compared to the typical values of 10-12 nm in the normal-incidence PLD grown films. Cross-sectional high resolution transmission electron microscope images revealed nanocolumnar growth of single-crystals of CFO along the (111) crystallographic plane at the film-substrate interface. Magnetic measurements showed larger coercive fields (â¼10 times) with similar saturation magnetization in the α-PLD-grown CFO thin films as compared to those deposited using normal-incidence PLD. Such significantly enhanced magnetic coercivity observed in CFO thin films make them ideally suited for magnetic data storage applications. A growth mechanism based on the atomic shadowing effect and strain compression-relaxation mechanism was proposed for the obliquely grown CFO thin films.
ABSTRACT
We report on the directed upright growth of ferroelectric (FE) Pb(Zr0.52Ti0.48)O3 (PZT) nanowire (NW) arrays with large aspect ratios of >60 using a Ti seed layer assisted hydrothermal process over large surface areas on ITO/glass substrates. In a two-step growth process, Ti seed layer of low surface roughness with a thickness of ~500 nm and grain size of ~100 nm was first deposited by radio frequency (RF) sputtering which was subsequently used as substrates for the growth of highly dense, single crystalline PZT NWs by controlled nucleation. The electron emission properties of the PZT NWs were investigated using the as-grown NWs as FE cathodes. A low turn-on field of ~3.4 V/µm was obtained from the NW arrays, which is impressively lower than that from other reported values. The results reported in this work give direction to the development of a facile growth technique for PZT NWs over large surfaces and also are of interest to the generation of high current electron beam from FE NW based cathodes for field emitter applications.
